Fantasizing about using usually starts with a negative feeling about sobriety. Frequently that negativity is caused by a wandering mind that thinks about worry and regret. Worry and regret involve thinking about the future and the past. The bottom line is that we need to live in today. Actually, we need to live in the now. Wondering about whether or not I am going to be able to stay sober at my high school reunion when I see all my drinking buddies for the first time in 30 years is a waste of time. I need to always focus on staying sober today, in this moment. When worries about how you are going to pay your taxes or regrets about why you invested in that stock bother you, you need to refocus on just doing the next right thing according to the four absolutes. If something needs to be planned, put it in your calendar, do whatever you need to do to prepare today, and then forget about it. If having a sobriety plan is necessary for that party, arrive late, leave early, have an escape plan, and remember you can always call your sponsor during the party.
If your mind slips into the past, ask yourself what you might have been able to learn from the experience, say the serenity prayer, then let it go. If you are endlessly debating about what decision to make, do a pros and cons list and a cost benefit analysis, tell yourself you never have a "crystal ball" that can magically reveal the perfect outcome, then make the decision and give the results to your Higher Power.
If you feel like relapsing or if you feel bad, it may be because your mind is wandering into the future or the past. Live one day at a time by refocusing wandering thoughts back to the moment. A good exercise is to do a few simple physical movements and have your mind trace these movements. For example, untie and retie your shoes while only thinking about untying and retying your shoes.